The soybean and "vegetable" off-flavor problem in textured vegetable protein has long been recognized. Many methods have been tried for the removal of this off-flavor, but none of the previous methods has been totally acceptable or successful. Such methods include heat treatment, steaming, acid treatment, and treatment with various solvents. It has now been found that supercritical fluid or liquefied gas extraction can be used to remove off-flavors from a textured vegetable product, particularly a textured soybean product.
A number of references utilize supercritical fluid gases or liquefied gases for the separation of organic materials or for flavor extraction. Supercritical fluid carbon dioxide has also been used for the removal of oil from soybeans. However, it appears that this technology has not been applied to a textured vegetable protein product.
U.S. Pat. No. 3,969,196, issued to Zosel (1976) discloses the supercritical fluid gas extraction of a mixture of organic substances. Zosel describes a number of organic compounds which can be extracted by supercritical fluid extraction, for example, aldehydes, ketones, alcohols, amines, esters and acids.
U.S. Pat. No. 3,477,856, issued to Schultz (1969) discloses liquid carbon dioxide extraction of flavors from fruits, vegetables or other plants. The flavor compounds include aldehydes, ketones, esters, and ethers. The patent suggests that supercritical fluid carbon dioxide extraction can also be used.
Canadian Pat. No. 1,014,571, issued to Vitzthum et al. (1977) describes supercritical fluid extraction of fat and oil from vegetable seed material. In particular, supercritical fluid carbon dioxide is used to extract oil from soybeans. Supercritical fluid carbon dioxide extraction of oil from soybeans is also disclosed in U.S. Pat. No. 4,466,923, issued to Friedrich (1984).
U.S. Pat. No. 4,427,707, issued to Heine et al. (1984) describes the extraction of unpleasant taste and odor components from locust beans and guar seeds using supercritical carbon dioxide.
None of these references suggests the use of a gas in the supercritical fluid or liquid state to extract off-flavors from textured vegetable product. Zosel's object is to provide a substitute for fractional distillation, not extraction of plants and plant materials. While Schultz discloses liquid carbon dioxide extraction of flavors from plants, the instant process involves extraction of off-flavor compounds from a textured vegetable product--not the native plant material. The emphasis of the Schultz patent is on isolating positive flavors from flavor-containing liquids--from fruits in particular.
Removal of off-flavors from textured soy product is also different from the method disclosed by Heine et al. The Heine et al. method for deflavoring locust beans and guar seeds would not be applicable in this invention since, as it will be shown later, hydration of the textured vegetable product prior to extraction is critical for off-flavor removal. There is no suggestion in the Heine et al. patent that moisture level is important.
Supercritical carbon dioxide extraction of oil from soybeans as taught by Friedrich requires higher temperatures and pressures (greater than 60.degree. C. and 7977 psia) than does the supercritical carbon dioxide extraction of textured soybean product off-flavor (greater than 31.degree. C. and 1070.6 psia). The textured soy product used in the process described herein is usually made from oil-free soy concentrate. In an article by Friedrich, Snyder, and Christianson, "Effect of Moisture and Particle Size on the Extractibility of Oils from Seeds with Supercritical CO.sub.2 ", JAOCS, Vol. 61, No. 12, pp. 1851-56 (1984), it is stated that moisture levels between 3% and 12% had little effect on extractability. This contrasts with the criticality of moisture level in the instant invention.
It is therefore an object of the instant invention to provide a method for the removal of off-flavors from a textured vegetable product by extraction with a gas in the supercritical fluid or liquid state.
It is another object to provide a method in which the textured vegetable product off-flavors are removed without altering texture.
These and other objects of this invention will become apparent by the description of the invention below.
All percentages are by weight unless otherwise defined.